NEW YORK Two Bosnian Serbs accused of planning and abetting "a campaign of terror" in the Balkans were released yesterday after an appeals chamber found the prosecutor of the U.N. war crimes tribunal had taken too long to begin the case against them.

This is the second time the appeals chamber has allowed an indictee to wait for his trial at home, a frustrated response to lengthy pretrial delays. The men, who flew home last night, are expected to return to the Hague-based tribunal when their trial is finally scheduled.

In February 1998, Simo Zaric and Miroslav Tadic surrendered to the International Criminal Tribunal for the Former Yugoslavia. The appeals chamber ordered their provisional release on April 4, but prosecutor Carla Del Ponte challenged their release, saying they were liable to flee.

In demanding the release yesterday, the appeals judges said the two accused have, "to date, been held in detention awaiting trial, for more than two years, and that there is no likelihood of an early date being fixed for the commencement of [their] trial."

U.N. officials have long been concerned about the sometimes glacial pace of the legal proceedings at the tribunals for the Balkans and Rwanda. An analysis in January found myriad reasons for pretrial delays, ranging from a shortage of chambers and judges to deliberate stalling by defense lawyers.

In releasing the two suspects yesterday, the judges said they were satisfied the two would return to the Hague-based tribunal when summoned, noting that they had surrendered voluntarily.

Mrs. Del Ponte vigorously fought the request to return Mr. Tadic and Mr. Zaric to their homes in Republika Srpska, as the Serb-ruled portion of Bosnia is now known.

"The prosecutor is concerned that the provisional release of these accused will have a very negative impact on the victims and witnesses in this case," said a statement released by her office yesterday afternoon.

"This concern is heightened by the fact that both accused were convicted and sentenced in absentia in March 1994 by the courts in Bosnia and Herzegovina, for offenses covered in the prosecutors' indictment before this tribunal."

Mr. Zaric, she noted, was originally sentenced to death.

Mrs. Del Ponte said she would ask international troops stationed in Bosnia to re-arrest the two if there was any indication they were interfering with witnesses or evidence.

But others were more supportive of the decision. Wolfgang Petritsch, the international community's senior representative in Bosnia, welcomed the release as "a step to build confidence between the government and The Hague."

Ben Ward, an investigator with Human Rights Watch, described the decision to release the two as a reasonable gamble.

"They are accused of very serious things, but no command responsibility and no murder," he said. "There is nothing to suggest that they are anything but entirely cooperative with the proceedings."

This is the second time Mrs. Del Ponte has opposed the provisional release of a suspect because her office has been unable to bring a trial forward swiftly. A former attorney general of Switzerland, Mrs. Del Ponte arrived at The Hague only six months ago.

In November, the appeals chamber ordered the release of Jean-Bosco Barayagwiza, a Rwandan media mogul and foreign ministry official who was accused of inciting the 1994 massacre of Tutsis.

After an outcry from the Rwandan government and vigorous opposition from Mrs. Del Ponte, the appeals judges reversed themselves last week and agreed to hold Mr. Barayagwiza for trial. Earlier this week his indictment was expanded to a total of nine counts, including crimes against humanity.

The U.N. report on delays in the trials, which was sent to the U.N. General Assembly's Budget Committee in January, made a number of recommendations to speed up trials and cut down delaying motions.

Tribunal officials are concerned that the delays will grow worse now that more indictees are in custody. Some trials, particularly those breaking new legal ground, could last as long as three years.